15
General layout of bus structure
Bus topology with terminating and bias resistors
Terminating resistor may only be installed at the ends of the bus line.
In networks with repeaters not more than two line terminations are allowed.
Line termination at the device can be activated via DIP switch 6.
The bias resistors for bus level definition in the resting state are usually activated at the Modbus master / repeater.
The maximum number of subscribers per Modbus segment is 32 devices.
When the number of subscribers is greater, the bus must be subdivided into several segments separated by repeaters.
The subscriber address can be set from 1 to 247.
For the bus line, a twisted-pair cable data line / power supply line and copper mesh wire shield must be used.
Therefore, the line capacitance should be less than 100 pF / m (e.g. Profibus cable).
G
THERMASGARD
®
RTM 1- Modbus
|
Installation
Rev. 2016 - V12 GB
intro
Slave n
MODBUS
RTU-Master
RS-485
Line
termination
Line
termination
Active
branch
Passive
branch
Stub line
Trunk line
Stub line:
shorter 20m
Multiple branch n:
shorter 40m/n
General layout of bus structure
Slave 1
Slave 2
LA
LA
Bus topology with terminating and bias resistors
A (D1) D+
5 V
Common
(GND)
B (D0) D–
Line
termination
Line
termination
Pull-down /
bias resistor
Pull-up /
bias resistor
MODBUS
RTU-Master
Slave 1
Slave 2
